With a good sand blast prior to welding Barry is right. I've done it a few times.
Thanks Vic for reminding folks that with welding, especially TIG, that the metal prep is paramont to having a decent weld that doesn't fall apart. Especially oil. There are special washes and preps but brake clean and good old soap and water with a good rinse due well and there are other special washes that can be used but, cost is a factor.